The invention relates to a method for offshore installation of a system for recovering hydrocarbons escaping from an underwater installation.
With the increasing number of offshore oil wells, there is an increasing risk of ecological accidents associated with hydrocarbons leaking from an underwater installation such as a wellhead or pipe, for example. The environmental consequences for the ecosystem can be irreversible and it is therefore necessary to intervene as quickly as possible to confine and recover the fluids escaping from the underwater installation in order to limit the environmental consequences linked to the outflow of these hydrocarbons into the marine environment.
To this end, it is known to deploy vertically above the damaged underwater installation bells having the shape of an inverted funnel to channel hydrocarbons escaping from the installation and recover them on a ship by means of a recovery pipe connecting the recovery bell and the hydrocarbon recovery ship.
Application WO2005/038145 in the name of the applicant discloses a recovery device comprising a rigid canopy of very large area intended to be deployed vertically over the underwater installation from which hydrocarbons are escaping. The area of the roof of the canopy is of the order of 100 to 10 000 m2. The canopy consists of two dihedral surfaces and is mounted on telescopic anchoring legs for stabilizing the position of the canopy over the underwater installation. It is connected to a flexible hydrocarbon raising pipe that is connected at the bottom to the canopy and extends up to the hydrocarbon recovery and storage ship. Moreover, a collecting chamber is disposed at the apex of the canopy, the flexible pipe being connected directly to the collecting chamber. There are carried out in the collecting chamber all operations beneficial to facilitating raising of the hydrocarbons, which may be very viscous and therefore difficult to raise to the surface via the pipe. These operations may consist in fluidizing the hydrocarbons by heating with electrical elements or by circulating hot water. They may also consist in diluting the hydrocarbons by adding dilutants or in mechanical stirring of the hydrocarbons in the collecting chamber. This recovery system is then towed to site and lowered in vertical alignment with the underwater installation, the buoyancy of the canopy being monitored and adjusted during its descent. The legs of the canopy are then deployed to stabilize the canopy on the seabed and vertically above the underwater installation.
A flexible pipe is then deployed from a pipelaying ship at the destination site. Unmanned submersibles are then used to connect the pipe to the collecting chamber and then to the surface installation.
The complete installation of such a recovery system may take months (two to three months) because it requires steps that are carried out in sequence and the sequential mobilization of a number of ships at the destination site.
These installation methods are therefore unsatisfactory because it is necessary to confine the leaking hydrocarbons as soon as possible to limit the impact on the environment.